1. Field of the Invention
The invention is relative to a device and a method of plaining in the art of glass manufacturing, or glass ceramics.
2. Description of the Related Art
Melting vats of continuous glass-melting furnaces are operated for the continuous plaining of glass that have a melting range, a plaining range and a standing and homogenizing range. The actual degassing of the glass melt customarily takes place in the plaining zone. Redox reactions or evaporation effects take place here that result in the formation of bubbles and in the inflating of present bubbles. The temperature in the plaining zone is selected to be as high as possible in order that the bubbles can rise rapidly to the surface of the melt and that the melt becomes bubble-free. Classic vats are limited thereby to maximum admissible temperatures in a plaining range of 1650xc2x0 C. on account of the wall material, that consist (as a rule) of fire-resistant ceramics or platinum or platinum alloys.
Numerous devices have become known with which glass can be melted or plained. See, e.g., EP 0,528,025 B1. It concerns a so-called skull crucible with a cooled crucible wall. The crucible wall is built up from a crown of vertical metal tubes that exhibit a mutual interval and through which a cooling medium flows. The crucible is surrounded by an induction coil through which high-frequency energy (HF) can be coupled into the crucible contents. In this manner the crucible contents can be brought to extremely high temperatures extending up to 3000xc2x0 C.
The plaining process requires especially high temperatures. Test have shown that the rising rate or speed of the bubbles distinctly increases as the melting temperature increases. Thus, high-temperature plaining creates the possibility of either drastically lowering the plaining time or of eliminating the addition of plaining media for producing large plaining bubbles. Rather high plaining temperatures would be particularly desirable in the case of high-melting glasses. The invention has an object of further developing a device and a method in accordance with the initially described type in such a manner that the plaining process is intensified.
This problem is solved by the features of the independent claims. The inventor has recognized that the plaining process can be designed to be significantly more efficient if it is not carried out in a single container, but rather in at least two containers connected in series. The quality of the glass is distinctly improved again if the melt is not only heated in the first plaining container to very high temperatures and then cooled off, but rather reheated in a second container and then allowed to cool off.
There is also the possibility, by connecting two plaining zones in series, that by allowing the two plaining processes that are taking place there to develop under different conditions and of using different plaining means at different locations additional benefits may be created.
The plaining containers can be standing skull crucibles or grooves (e.g., channels). A standing skull crucible can also be combined with a groove. The groove can likewise be designed in the manner of a skull crucible. The crucible is built in any case, from a crown of metal tubes that are connected to a cooling medium. They are completely surrounded in any case by the windings of a HF coil.
If the cooled metal tubes of the groove run horizontally, the windings of the HF coil are to be placed in such a manner around the tubes that the crucible axis run horizontally. However, if the cooled metal tubes are arranged to be standing, the windings of the HF coil are placed around the tubes in such a manner that the central axis runs substantially vertically.
A device for plaining glasses and glass-ceramics comprising a melting vat, at least two plaining containers serially connected at the output end of said melting vat, and at least one of the plaining containers is built up according to the skull principle from a plurality of metal tubes comprising, for their part, a cooling-agent connection and from a high-frequency device for inductively coupling high-frequency energy into the contents of the plaining container.
A method for the plaining of glasses or glass-ceramics comprising the steps of:
Melting the substances; and then
Plaining in a plaining cascade consisting of two or more stages, in which the plaining takes place in at least one of these stages according to the skull principle with inductive heating of the melt by radiating high-frequency energy.